RIFF WAVE (.WAV) file format
----------------------------
From: Rob Ryan
Organization: Brown University
I found the following lengthy excerpt in a document rmrtf.zrt (it is actually
a .zip file) in the vendor/microsoft/multimedia subdirectory at the ftp.uu.net
ftp site. It is presumably beyond the scope (in terms of the amount of
detail) of your document, but nevertheless, I thought that it may help you
in including references to the Windows .WAV format in the future.
Let me know if you have any questions/comments. Again, thank you for your
helpful summary. Keep it up!
The following is taken from RIFFMCI.RTF, "Multimedia Programming Interface
and Data Specification v1.0", a Windows RTF (Rich Text Format) file contained
in the .zip file, RMRTF.ZRT. The original document is quite long and this
constitutes pages 83-95 of the text format version (starting on roughly
page 58 of the RTF version). If you would like a PostScript version, let
me know and I can make one up for you.
Waveform Audio File Format (WAVE)
This section describes the Waveform format, which is used to
represent digitized sound.
The WAVE form is defined as follows. Programs must expect
(and ignore) any unknown chunks encountered, as with all
RIFF forms. However, must always occur before
, and both of these chunks are mandatory in a
WAVE file.
->
RIFF( 'WAVE'
// Format
[] // Fact chunk
[] // Cue points
[] // Playlist
[] // Associated
data list
) // Wave data
The WAVE chunks are described in the following sections.
WAVE Format Chunk
The WAVE format chunk specifies the format of the
. The is defined as follows:
-> fmt( )
->
struct
{
WORD wFormatTag; // Format category
WORD wChannels; // Number of channels
DWORDdwSamplesPerSec; // Sampling rate
DWORDdwAvgBytesPerSec; // For buffer
estimation
WORD wBlockAlign; // Data block size
}
The fields in the chunk are as follows:
Field Description
wFormatTag A number indicating the WAVE format
category of the file. The content of
the portion
of the `fmt' chunk, and the
interpretation of the waveform data,
depend on this value.
You must register any new WAVE format
categories. See ``Registering
Multimedia Formats'' in Chapter 1,
``Overview of Multimedia
Specifications,'' for information on
registering WAVE format categories.
``Wave Format Categories,'' following
this section, lists the currently
defined WAVE format categories.
wChannels The number of channels represented in
the waveform data, such as 1 for mono
or 2 for stereo.
dwSamplesPerSe The sampling rate (in samples per
c second) at which each channel should
be played.
dwAvgBytesPerS The average number of bytes per second
ec at which the waveform data should be
transferred. Playback software can
estimate the buffer size using this
value.
wBlockAlign The block alignment (in bytes) of the
waveform data. Playback software needs
to process a multiple of wBlockAlign
bytes of data at a time, so the value
of wBlockAlign can be used for buffer
alignment.
The consists of zero or more bytes
of parameters. Which parameters occur depends on the WAVE
format category-see the following section for details.
Playback software should be written to allow for (and
ignore) any unknown parameters that
occur at the end of this field.
WAVE Format Categories
The format category of a WAVE file is specified by the value
of the wFormatTag field of the `fmt' chunk. The
representation of data in , and the content of
the of the `fmt' chunk, depend on
the format category.
The currently defined open non-proprietary WAVE format
categories are as follows:
wFormatTag Value Format Category
WAVE_FORMAT_PCM (0x0001) Microsoft Pulse Code
Modulation (PCM) format
The following are the registered proprietary WAVE format
categories:
wFormatTag Value Format Category
IBM_FORMAT_MULAW IBM mu-law format
(0x0101)
IBM_FORMAT_ALAW (0x0102) IBM a-law format
IBM_FORMAT_ADPCM IBM AVC Adaptive
(0x0103) Differential Pulse Code
Modulation format
The following sections describe the Microsoft
WAVE_FORMAT_PCM format.
Pulse Code Modulation (PCM) Format
If the wFormatTag field of the is set to
WAVE_FORMAT_PCM, then the waveform data consists of samples
represented in pulse code modulation (PCM) format. For PCM
waveform data, the is defined as
follows:
->
struct
{
WORD wBitsPerSample; // Sample size
}
The wBitsPerSample field specifies the number of bits of
data used to represent each sample of each channel. If there
are multiple channels, the sample size is the same for each
channel.
For PCM data, the wAvgBytesPerSec field of the `fmt' chunk
should be equal to the following formula rounded up to the
next whole number:
wBitsPerSample
wChannels x wBitsPerSecond x --------------
8
The wBlockAlign field should be equal to the following
formula, rounded to the next whole number:
wBitsPerSample
wChannels x --------------
8
Data Packing for PCM WAVE Files
In a single-channel WAVE file, samples are stored
consecutively. For stereo WAVE files, channel 0 represents
the left channel, and channel 1 represents the right
channel. The speaker position mapping for more than two
channels is currently undefined. In multiple-channel WAVE
files, samples are interleaved.
The following diagrams show the data packing for a 8-bit
mono and stereo WAVE files:
Sample 1 Sample 2 Sample 3 Sample 4
Channel 0 Channel 0 Channel 0 Channel 0
Data Packing for 8-Bit Mono PCM
Sample 1 Sample 2
Channel 0 Channel 1 Channel 0 Channel 0
(left) (right) (left) (right)
Data Packing for 8-Bit Stereo PCM
The following diagrams show the data packing for 16-bit mono
and stereo WAVE files:
Sample 1 Sample 2
Channel 0 Channel 0 Channel 0 Channel 0
low-order high-order low-order high-order
byte byte byte byte
Data Packing for 16-Bit Mono PCM
Sample 1
Channel 0 Channel 0 Channel 1 Channel 1
(left) (left) (right) (right)
low-order high-order low-order high-order
byte byte byte byte
Data Packing for 16-Bit Stereo PCM
Data Format of the Samples
Each sample is contained in an integer i. The size of i is
the smallest number of bytes required to contain the
specified sample size. The least significant byte is stored
first. The bits that represent the sample amplitude are
stored in the most significant bits of i, and the remaining
bits are set to zero.
For example, if the sample size (recorded in nBitsPerSample)
is 12 bits, then each sample is stored in a two-byte
integer. The least significant four bits of the first (least
significant) byte is set to zero.
The data format and maximum and minimums values for PCM
waveform samples of various sizes are as follows:
Sample Size Data Format Maximum Value Minimum Value
One to Unsigned 255 (0xFF) 0
eight bits integer
Nine or Signed Largest Most negative
more bits integer i positive value of i
value of i
For example, the maximum, minimum, and midpoint values for
8-bit and 16-bit PCM waveform data are as follows:
Format Maximum Minimum Value Midpoint
Value Value
8-bit PCM 255 (0xFF) 0 128 (0x80)
16-bit PCM 32767 -32768 0
(0x7FFF) (-0x8000)
Examples of PCM WAVE Files
Example of a PCM WAVE file with 11.025 kHz sampling rate,
mono, 8 bits per sample:
RIFF( 'WAVE' fmt(1, 1, 11025, 11025, 1, 8)
data( ) )
Example of a PCM WAVE file with 22.05 kHz sampling rate,
stereo, 8 bits per sample:
RIFF( 'WAVE' fmt(1, 2, 22050, 44100, 2, 8)
data( ) )
Example of a PCM WAVE file with 44.1 kHz sampling rate,
mono, 20 bits per sample:
RIFF( 'WAVE' INFO(INAM("O Canada"Z))
fmt(1, 1, 44100, 132300, 3, 20)
data( ) )
Storage of WAVE Data
The contains the waveform data. It is defined as
follows:
-> { : }
-> data( )
-> LIST( 'wavl' { :
// Wave samples
}... ) // Silence
-> slnt( ) // Count
of
// silent samples
Note: The `slnt' chunk represents silence, not necessarily
a repeated zero volume or baseline sample. In 16-bit PCM
data, if the last sample value played before the silence
section is a 10000, then if data is still output to the D to
A converter, it must maintain the 10000 value. If a zero
value is used, a click may be heard at the start and end of
the silence section. If play begins at a silence section,
then a zero value might be used since no other information
is available. A click might be created if the data following
the silent section starts with a nonzero value.
FACT Chunk
The fact chunk stores important information about
the contents of the WAVE file. This chunk is defined as
follows:
-> fact( ) // Number
of samples
The `fact'' chunk is required if the waveform data is
contained in a `wavl'' LIST chunk and for all compressed
audio formats. The chunk is not required for PCM files using
the `data'' chunk format.
The "fact" chunk will be expanded to include any other
information required by future WAVE formats. Added fields
will appear following the field. Applications
can use the chunk size field to determine which fields are
present.
Cue-Points Chunk
The cue-points chunk identifies a series of
positions in the waveform data stream. The is
defined as follows:
-> cue( // Count of cue
points
... ) // Cue-point
table
-> struct {
DWORD dwName;
DWORD dwPosition;
FOURCC fccChunk;
DWORD dwChunkStart;
DWORD dwBlockStart;
DWORD dwSampleOffset;
}
The fields are as follows:
Field Description
dwName Specifies the cue point name. Each
record must have a unique
dwName field.
dwPosition Specifies the sample position of the
cue point. This is the sequential
sample number within the play order.
See ``Playlist Chunk,'' later in this
document, for a discussion of the play
order.
fccChunk Specifies the name or chunk ID of the
chunk containing the cue point.
dwChunkStart Specifies the file position of the
start of the chunk containing the cue
point. This is a byte offset relative
to the start of the data section of
the `wavl' LIST chunk.
dwBlockStart Specifies the file position of the
start of the block containing the
position. This is a byte offset
relative to the start of the data
section of the `wavl' LIST chunk.
dwSampleOffset Specifies the sample offset of the cue
point relative to the start of the
block.
Examples of File Position Values
The following table describes the field values
for a WAVE file containing multiple `data' and `slnt' chunks
enclosed in a `wavl' LIST chunk:
Cue Point Field Value
Location
In a `slnt' fccChunk FOURCC value `slnt'.
chunk
dwChunkStart File position of the
`slnt' chunk relative to
the start of the data
section in the `wavl' LIST
chunk.
dwBlockStart File position of the data
section of the `slnt'
chunk relative to the
start of the data section
of the `wavl' LIST chunk.
dwSampleOffs Sample position of the cue
et point relative to the
start of the `slnt' chunk.
In a PCM fccChunk FOURCC value `data'.
`data' chunk
dwChunkStart File position of the
`data' chunk relative to
the start of the data
section in the `wavl' LIST
chunk.
dwBlockStart File position of the cue
point relative to the
start of the data section
of the `wavl' LIST chunk.
dwSampleOffs Zero value.
et
In a fccChunk FOURCC value `data'.
compressed
`data' chunk
dwChunkStart File position of the start
of the `data' chunk
relative to the start of
the data section of the
`wavl' LIST chunk.
dwBlockStart File position of the
enclosing block relative
to the start of the data
section of the `wavl' LIST
chunk. The software can
begin the decompression at
this point.
dwSampleOffs Sample position of the cue
et point relative to the
start of the block.
The following table describes the field values
for a WAVE file containing a single `data' chunk:
Cue Point Field Value
Location
Within PCM fccChunk FOURCC value `data'.
data
dwChunkStart Zero value.
dwBlockStart Zero value.
dwSampleOffs Sample position of the cue
et point relative to the
start of the `data' chunk.
In a fccChunk FOURCC value `data'.
compressed
`data' chunk
dwChunkStart Zero value.
dwBlockStart File position of the
enclosing block relative
to the start of the `data'
chunk. The software can
begin the decompression at
this point.
dwSampleOffs Sample position of the cue
et point relative to the
start of the block.
Playlist Chunk
The playlist chunk specifies a play order for
a series of cue points. The is defined as
follows:
-> plst(
// Count of play
segments
... ) // Play-segment
table
-> struct {
DWORD dwName;
DWORD dwLength;
DWORD dwLoops;
}
The fields are as follows:
Field Description
dwName Specifies the cue point name. This
value must match one of the names
listed in the cue-point
table.
dwLength Specifies the length of the section in
samples.
dwLoops Specifies the number of times to play
the section.
Associated Data Chunk
The associated data list provides the
ability to attach information like labels to sections of the
waveform data stream. The is defined as
follows:
-> LIST('adtl'
// Label
// Note
// Text
with data length
) // Media
file
-> labl( )
-> note( )
-> ltxt(... )
-> file(...)
Label and Note Information
The `labl' and `note' chunks have similar fields. The `labl'
chunk contains a label, or title, to associate with a cue
point. The `note' chunk contains comment text for a cue
point. The fields are as follows:
Field Description
dwName Specifies the cue point name. This
value must match one of the names
listed in the cue-point
table.
data Specifies a NULL-terminated string
containing a text label (for the
`labl' chunk) or comment text (for the
`note' chunk).
Text with Data Length Information
The `ltxt'' chunk contains text that is associated with a
data segment of specific length. The chunk fields are as
follows:
Field Description
dwName Specifies the cue point name. This
value must match one of the names
listed in the cue-point
table.
dwSampleLength Specifies the number of samples in the
segment of waveform data.
dwPurpose Specifies the type or purpose of the
text. For example, dwPurpose can
specify a FOURCC code like `scrp' for
script text or `capt' for close-
caption text.
wCountry Specifies the country code for the
text. See ``Country Codes'' in Chapter
2, ``Resource Interchange File
Format,'' for a current list of
country codes.
wLanguage, Specify the language and dialect codes
wDialect for the text. See ``Language and
Dialect Codes'' in Chapter 2,
``Resource Interchange File Format,''
for a current list of language and
dialect codes.
wCodePage Specifies the code page for the text.
Embedded File Information
The `file' chunk contains information described in other
file formats (for example, an `RDIB' file or an ASCII text
file). The chunk fields are as follows:
Field Description
dwName Specifies the cue point name. This
value must match one of the names
listed in the cue-point
table.
dwMedType Specifies the file type contained in
the fileData field. If the fileData
section contains a RIFF form, the
dwMedType field is the same as the
RIFF form type for the file.
This field can contain a zero value.
fileData Contains the media file.